Effect of heat treatment on thermal and mechanical stability of NaOH-doped xanthan gum-based hydrogels

Abstract

Xanthan gum (XG)-based hydrogels containing sodium hydroxide (NaOH) salt were synthesized with the use of distilled water (DW) at room temperature and characterized through FTIR, TGA/DTG, and rheological studies. Sodium hydroxide is used to control pH toward neutral region along with improvement in ionic conductivity and stability of the electrolyte. The stabilized hydrogel has been obtained by applying heat treatment at ambient temperature for 5 wt% XG in 0.015 M solution of NaOH, which exhibits nearly neutral pH value at room temperature. The modification/shifting of the various peaks in FTIR spectra of xanthan gum with the addition of salt indicates the interaction or cross-linking between the constituents (xanthan gum, distilled water, and NaOH) and disappearing of peaks after heat treatment of the gel confirms its stability. DTG and TGA studies have been carried out to investigate thermal stability of these gels and illustrate the effect of heat treatment as a result of salt addition with thermogravimetric analysis up to 400 °C. However, rheological studies were performed for these hydrogels to analyze their viscosity behavior and mechanical stability. Along with the above characterization, gel sample (5 wt% XG in 0.015 M NaOH solution in DW) exhibits high ionic conductivity of 4.71 × 10−3 S/cm with 6.45 pH value at room temperature after heat treatment. These highly ion conducting, thermally and mechanically stable biodegradable xanthan gum-based hydrogels can also be used as an electrolyte for various device applications like supercapacitors, fuel cells, solar cells, etc.